Horizontal simulation grids as alternative to structure-based grids for thin oil-zone problems: a comparison study on a Troll segment |
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| Authors: | ?ystein Pettersen |
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| Institution: | (1) National Energy Technology Laboratory, Pittsburgh, PA 15236, USA; |
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| Abstract: | The layering in reservoir simulation grids is often based on the geology, e.g., structure tops. In this paper we investigate
the alternative of using horizontal layers, where the link to the geology model is by the representation of the petrophysics
alone. The obvious drawback is the failure to honor the structure in the grid geometry. On the other hand, a horizontal grid
will honor the initial fluid contacts perfectly, and horizontal wells can also be accurately represented. Both these issues
are vital in thin oil-zone problems, where horizontal grids may hence be a viable alternative. To investigate this question,
a number of equivalent simulation models were built for a segment of the Troll Field, both geology-based and horizontal, and
various combinations of these. In the paper, it is demonstrated that the horizontal grid was able to capture the essentials
of fluid flow with the same degree of accuracy as the geology-based grid, and near-well flow was considerably more accurate.
For grids of comparable resolution, more reliable results were obtained by a horizontal grid than a geo-grid. A geo-grid with
local grid refinement and a horizontal grid produced almost identical results, but the ratio of computing times was almost
20 in favor of the horizontal grid. In the one-phase regions of the reservoir, relatively coarse cells can be used without
significant loss of accuracy. |
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